1. Field of the Invention
The present invention relates to a group III-nitride light emitting device and a manufacturing method thereof. More particularly, the present invention relates to a vertical group III-nitride light emitting device improved in light extraction efficiency, and a manufacturing method thereof.
2. Description of the Related Art
Since development of a light emitting diode (LED) including a group III-nitride semiconductor, it has been utilized as a light source in a variety of areas such as a liquid crystal display (LCD) backlight, a mobile phone keypad, a illumination lighting source and the like. Regarding development of the LED for wide-ranging purposes, light-emitting efficiency and heat releasing properties thereof have emerged as a significant factor. Light-emitting efficiency of the LED is determined by light generation efficiency, external extraction efficiency and amplification efficiency by fluorescent material. Most of all, the biggest problem concerns low external extraction efficiency, that is, light generated is externally extracted at a low efficiency. The greatest hurdle against light extraction out of the LED is extinction of light resulting from total internal reflection. That is, big refractivity differences at an interface of the LED allows only about 20% of light generated to exit outside the interface of the LED. The light totally reflected at the interface travels inside the LED and is reduced to heat. This increases a heat release rate of the LED, and decreases external extraction efficiency of the LED, thus shortening lifetime thereof.
To overcome this problem, suggestions have been made regarding methods for improving external extraction efficiency. For example, a surface pattern or a surface texture is formed on the LED to enable a photon arriving at its surface to scatter randomly. Alternatively, the light emitting device is shaped as a truncated inverted pyramid. Furthermore, in another recent method, to form a photonic crystal, the LED surface is patterned such that a photon of a specified wavelength is transmitted or reflected selectively. Also, a thick sapphire substrate can be removed from the LED structure after attaching a metal substrate to the LED structure. For now, the vertical GaN-based LED obtained thereby exhibits the highest extraction efficiency. “Watt-Class High-Output-Power 365 nm Ultraviolet Light-Emitting Diodes” by Daisuke Morita et al. published in Japanese Journal of Applied Physics (Vol. 43, No. 9A, 2004, pp. 5945-5950) discloses a vertical GaN-based LED having a rough pattern on an n-AlGaN contact layer and a manufacturing method thereof.
FIG. 1 is a side sectional view illustrating an example of a conventional vertical group III-nitride light emitting device. Referring to FIG. 1, the conventional group III-nitride light-emitting device 10 includes a conductive adhesive layer 12, a metal reflective layer 13, a p-doped AlGaN contact layer 14, a p-doped AlGaN clad layer 15, an active layer 16 and an n-doped AlGaN contact layer 17 sequentially stacked on a conductive substrate 11. Also, an n-electrode 18 is formed on the n-doped AlGaN contact layer 17.
As shown in FIG. 1, a rough pattern 21 is formed on the n-doped AlGaN contact layer 17 exposed to an outside. A photon which starts from inside the light emitting device 10 and arrives at the rough pattern 21 is scattered in the rough pattern 21, thus more highly likely to exit to the outside. Eventually, despite big refractivity differences between AlGaN material and external environments such as air and epoxy resin, external extraction efficiency can be improved.
However, in the conventional vertical group III-nitride light emitting device 10, to enable sufficient extraction of light through the rough pattern 21, a contact area of the n-electrode 18 becomes a relatively small. Accordingly, current concentrates in a lower part of the n-electrode 18, disadvantageously increasing operating voltage Vf of the light emitting device 10.
Further, to manufacture the conventional vertical group III-nitride light emitting device 10 having the rough pattern 21 requires following processes to be conducted sequentially: growing GaN-based semiconductor 17, 16, 15, 14 on a sapphire substrate (not illustrated), adhering the conductive substrate 11, removing the sapphire substrate and forming the rough pattern 21. In addition, to form the rough pattern 21 requires a photolithography process including wet or dry etching such as inductivity coupled plasma-reactive ion etching (ICP-RIE) on the n-doped AlGaN contact layer 17. However, with the sapphire substrate removed, it is very difficult to perform the photolithography on a top surface of a thin-filmed GaN-based structure having a thickness of 10 μm or less, even though the conductive substrate 11 is used as a supporting substrate. Accordingly, this leads to significant decrease in yield.